Historically, it has often been important to determine the amount of a given contaminant or foreign substance present in a given product. For example, determinations of this nature can be vitally important if a product, during manufacture, needs to be screened in order that unduly contaminated portions thereof can be safely rejected and prevented from reaching the consumer public. Some examples of products in which such determinations might be important are, but are not limited to, the following: clear solvents (such as alcohol, paint thinner, turpentine, etc.); liquid pharmaceutical or medicinal products (e.g. liquid cold/fever medicines, hydrogen peroxide, liquids for use in vaporizers); various clear or "dye-free" products in the market place (including, among others, liquid soaps, detergents and waxes, shampoos, hair sprays, cosmetics, deodorants, topical medications, beverages, ingestible and parenteral alimentation solutions); fossil fuels, such as petroleum (either in crude or refined form); and other liquids which may either be essentially clear in nature or may have a given base color.
As another example, in the context of medicine and physiology, there has often been a need to accurately determine the levels of certain substances, which may be considered "contaminants", in a given portion of a patient's bodily fluids. Such substances may be foreign to or naturally occurring in the human body. They may be innately undesirable or physiologically beneficial. By way of example, a brief discussion of red blood cells as a possible "contaminant" in certain contexts is provided herebelow.
Normally, human blood will contain a quantity of red blood cells and a quantity of white blood cells, in addition to other components. Historically, it has often been important to measure, with some accuracy, the presence of these constituent portions in a patient's blood, in order to assist, for example, in the diagnosis of given diseases or disorders.
One convenient parameter for assessing the relative presence of different constituents in a sample of patient's blood is the hematocrit parameter. Nominally, the hematocrit parameter will indicate, with some degree of accuracy, the degree to which the volume of the patient's blood is accounted for by red blood cells. Generally, the hematocrit value can be expressed as a percentage or a decimal proportion, or by any other means for clearly expressing such a ratio or proportion. Thus, the hematocrit of a blood sample or blood product sample can be considered, for most purposes, as being roughly equivalent to the percentage (by volume) of the blood or blood product sample that is constituted by red blood cells.
Conventionally, hematocrit measurements have often been determined for whole-blood samples, i.e. blood samples withdrawn directly from a patient which are not subject to subsequent separation, treatment or other modification. In addition, however, a tremendous value has often been placed on measuring hematocrit values with regard to a blood sample that has itself already undergone some type of modification or alteration, such as blood products, having been selectively extracted from a whole blood sample, that contain, for instance, a preponderance of white blood cells. In such instances, it is often extremely vital to ensure that hematocrit levels will not be excessively high, or, more particularly, that they will not exceed a predetermined threshold. It is in such instances that, for practical purposes, the red blood cells may be viewed as a "contaminant".
In the context of blood products containing a preponderance of white blood cells, the need for accuracy in hematocrit measurements has been widely recognized. Particularly, it has been widely recognized that the acceptable margin of error in taking hematocrit measurements of blood products containing a preponderance of white blood cells is tremendously smaller than in the case of measuring whole-blood samples. Therefore, even though a margin of error built into a given measuring apparatus or process might arguably have a negligible effect in the context of whole blood samples (e.g., blood samples in which the hematocrit value is on the order of magnitude of 50% or higher), it would, in proportion to the actual hematocrit values present, be much more significant in the context of a blood sample containing a preponderance of white blood cells (e.g., a blood sample having a hematocrit value on the order of magnitude of only a few percent or less).
The need for a high degree of accuracy at low levels of hematocrit might be especially important in order to properly diagnose or verify a particular disorder or disease the patient might have in order to provide proper treatment for the patient. For example, if a blood sample is extracted from a patient, and then is subsequently separated in a centrifuge or other cell separating device, it might be extremely important to ensure that the hematocrit level is sufficiently low in order for the blood sample to be able to undergo subsequent treatment, such as irradiation in an irradiation apparatus. In this vein, it is a distinct possibility that an unduly high level of hematocrit in a patient's blood sample (i.e., a blood sample containing a preponderance of white blood cells), even on the order of magnitude of a few tenths of a percentage point or less, could subsequently result in relatively ineffective treatment (thus either delaying or even jeopardizing the possibility of the patient's recovery), or could simply represent an undesirable waste of time and resources (in that a complete restart of the procedures of withdrawing, centrifuging and treatment might be necessary).
Conventionally, one method of measuring hematocrit involves the centrifuging of a sample with a standard centrifuge and a capillary tube. A physical measurement is made of packed red cells in the tube, and a hematocrit calculation is derived therefrom. However, disadvantages are found in that the blood must first be collected and then centrifuged, and in that results are generally not immediately available. Further, results tend not to be highly accurate at lower hematocrit levels, such as hematocrit levels of about 30% or less.
Another conventional method contemplates a technique in which two LED (light-emitting diode) emitters of differing wavelength (typically red [i.e., generally about 600 nm] and green [i.e., generally about 500 nm]) are modulated through a sampling cuvette. A photodiode and electrical circuit amplify the light that has originated from the emitter and passed through the cuvette. Once the LED has been switched on and permitted to stabilize, a measurement is made of the difference in the signal amplitude of the modulated light. A computer calculates the hematocrit measurement based differences in the light reaching the detector. Results obtained in connection with such systems tend not to be accurate with respect to blood products samples having significantly low hematocrit levels (such as about 6% or less), and response time tends to be slow in view of the use of modulated light and in view of the response time of the photodiode circuit. These systems tend to be highly complex in view of the light modulation technique and the need to compute the difference between two detector readings.
U.S. Pat. No. 5,351,686 to Steuer et al. discloses an arrangement in which a disposable cuvette, through which pulsatile flowing blood is to pass, has a conduit with two opposed walls having a predetermined separation therebetween that varies with each pulse of the flowing blood. In this procedure, it is possible to produce a value indicative of the change in a patient's hematocrit from one point in time to another, as well as values indicating absolute hematocrit. However, since this patent to Steuer et al. appears only to contemplate the detection of hematocrit in whole blood, it would appear that the apparatus disclosed therein may not be as accurate as desired at relatively low levels of hematocrit (as discussed more generally heretofore).
U.S. Pat. No. 5,372,136 to Steuer et al. discloses a system and method for hematocrit monitoring in which, for example, a finger may be inserted into a tube-like structure or a clip may be placed on an earlobe. In either case, a photodiode arrangement assists in the determination of a hematocrit value on the basis of the extinction of various wavelengths of light that have traveled through the human body part in question. This procedure involves what may be called a "non-invasive" detection of hematocrit. However, it only appears to be capable of determining a value indicative of a change in a patient's hematocrit from one point in time to another, and not absolute values of hematocrit. Further, the apparatus disclosed in this patent to Steuer et al. would also appear to encompass similar disadvantages as described immediately above and more generally heretofore (that is, it may not be as accurate as desired at low levels of hematocrit). Additionally, there would also appear to be a potential distorting factor arising from the passage of light through additional, intervening media, e.g., the patient's skin, bone, muscle and other bodily components.
It is believed that the known devices and processes discussed and alluded to hereinabove, for the most part, are complex and expensive, and present results that are not as accurate as may be desired.
In view of the foregoing, a need has arisen for the provision of a detector or detectors that can, in the presence of a given liquid containing an undesirable substance or contaminant therewithin, accurately ascertain the degree of the contaminant's presence.